Wanna go fast

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Active Member

So, after attending the local wanna go fast at Travolta's airstrip here in Ocala, FL I'm thinking I want to see what the GN will do in the 1/2 mile. I typed several terms in the search engine here looking for car prep advice to no avail. So, I'm asking; What should I do to prep the GN for all out 1/2 mile run?

I have read that air from the intercooler will gather under the hood and lift the front end, so I plan to remove the weatherstrip at the cowl. Also plan to remove center caps so I don't lose them.

On a mild tune at 18 pounds the car made 341hp and 373ft# to the rear wheels so I am not planning to go 200 mph but don't want to get into any loose handling issues if I can help it.
Thanks

What you read is correct, but they omitted that a high pressure area forms at the base of the windshield. If you remove that wheather strip, you'll pressurize the engine bay even worse and stall flow through the radiator.

GNX fender vents (with the repop internal duct kit) actually work, though their size limits flow a lot. Better than nothing. A hood with extractor vents in a low pressure spot further forward will also work. A piece of flat lexan covering the headlight buckets will help, too. But removing that weather strip will not work the way you're thinking at high speed.

The big fix for top speed is an air/water intercooler and get rid of that IC scoop completely.

Also be aware of boost creep. It might be rock solid at your setpoint for 1420 feet, but adding another 1420 to that and it cloud creep on you. Keep an eye on the boost and knock counter.

Member

As i was sitting at work the other day looking at some v series caddy's and a zr1 vette , it got me thinking , has anyone every tried to come up with a hood extractor for our cars?
i remember back a while ago Lawrence Conley used what looked like gnx vents on the hood but i was thinking something a little more modern then that. i know the crowd here is more drag racing but something like that may even help them.

Active Member

1/4 miles races are very hard on your car, esp. if it is not in top running form. A half mile or more at full throttle will do major damage if this ride isnt in perfect running order. From what i can tell the guys running the kind of speed your looking to get,130 have all out well built race cars. They handle for shit to begin with. I dont know if your car is stock or not but i would be very hesitant about going full throttle for over half a mile just to see what top end is. Good luck, saftey first.

Active Member

Seriously though, the OP is not running the Texas mile, nor Bonneville nor a flat-out top speed test. He's asking about a half mile.

I would start with some way to calculate what your theoretical speed should be at the half mile and what rpm you might be at. That alone might tell you, to Gene's point, whether the motor will be in jeopardy or not at that rpm.

Also, you may be able to determine if you are in any aerodynamic jeopardy at this expected speed. If so, back out or think about the changes needed as others here have alluded to in order to run safely.

If ok, let's move on to stability and safety. Suspension, steering, wheels, tires, etc. Anything that makes the connection from car to ground. If it's not perfectly safe, I'd abort the idea. Maximizing all of these things to yield a better speed at the half mile is a different story. Not sure if you're looking to go to that extent or not.

Based on the way our cars run and the gear and rpm I'd guess at the half mile point, you will either just make it there without revving out to an unsafe level or if the estimates suggest you will reach rpm limits, you could change the gears.

Active Member

Quick search shows rough rule of thumb that your 1 mile speed is 1.33 times your quarter mile trap speed. My car makes a little more rwhp than yours and based on my trap speed of about 114, my car would hit (theoretically) 152mph in the mile, which means my car gains 38 mph after the quarter mile or about 12-13 mph per quarter mile after the first quarter mile. So, roughly, my car will reach 126-127 at the half mile, probably a hair more because the gain is not linear, quarter by quarter, but more on a curve with a better gain earlier rather than later (each quarter mile you gain less) assuming power curves remain constant which of course they usually don't so the curve gets even worse later.

Active Member

All good points (except SpeedracerX post about painting the car gold with a miller beer logo Front end lift is what concerns me most. I am not crazy about cutting up my hood for a one time run (or 2-3 runs on a single day). If this was something I wanted to do on a regular basis, I'd build the car with more purpose... Roll bar, heat extractors, 5 point shoulder harnesses and sticky tires on all 4 corners... the list is endless. But it is a street car that I drive when the weather is nice.
Maybe I will shelf this idea for a bit.

Short Guy

As i was sitting at work the other day looking at some v series caddy's and a zr1 vette , it got me thinking , has anyone every tried to come up with a hood extractor for our cars?
i remember back a while ago Lawrence Conley used what looked like gnx vents on the hood but i was thinking something a little more modern then that. i know the crowd here is more drag racing but something like that may even help them.

You can get them made. VFN Fiberglass has a hood for our cars, and sells extractor vents and will put them in the hood for you.

The trick is figuring out where to put the vents. You can use a magnehelic gauge with the probe taped to various spots on the hood. Get up to highway speed, note the pressure. Move it, test again.

Once you find the spot on the hood with the lowest pressure, that's where you cut for your vent.

I haven't done it yet, but a fiberglass hood with extractor vents is on my to-do list for next year. If they're in the right place and big enough, they will likely mitigate front end lift in speed ranges I'm expecting to see at NCM or Putnam. Engine temps will fall, too. Fab some kind of splitter and undertray to go with it and the car could be good past 150.

Member

You can get them made. VFN Fiberglass has a hood for our cars, and sells extractor vents and will put them in the hood for you.

The trick is figuring out where to put the vents. You can use a magnehelic gauge with the probe taped to various spots on the hood. Get up to highway speed, note the pressure. Move it, test again.

Once you find the spot on the hood with the lowest pressure, that's where you cut for your vent.

I haven't done it yet, but a fiberglass hood with extractor vents is on my to-do list for next year. If they're in the right place and big enough, they will likely mitigate front end lift in speed ranges I'm expecting to see at NCM or Putnam. Engine temps will fall, too. Fab some kind of splitter and undertray to go with it and the car could be good past 150.

Thanks so much for that info - i appreciate the time to answer my inquiry
i would also love to hear how your hood goes , please keep us informed of how it is going
i dont know if im going to get to mine this year but maybe ill put it on the list for next year

Short Guy

Thanks so much for that info - i appreciate the time to answer my inquiry
i would also love to hear how your hood goes , please keep us informed of how it is going
i dont know if im going to get to mine this year but maybe ill put it on the list for next year

I have to get through an engine build first, and brakes, and I'm doing bumpers before the hood because there's a lot more weight to be saved and I spend a lot more time yanking it around a parking lot at 60 or less than on a road course at 120+.

But the hood might happen by mid-year. I'll certainly post results if/when I get it done.

Short Guy

Full results in the post, but what I found was the best place to put a vent, from a pressure standpoint, is in the middle just ahead of the bulge.

The GNX fender location was not good. Up closer to the windshield alongside the bulge also was not good. And, I verified that a high pressure area forms at the cowl, so removing the weather strip will in fact NOT have a positive affect on airflow through the engine bay at speed.

Numbers are KPA/100, the reference port (0) was inside the car, so negative means pressure below the reference.
Here's the grid we measured. We placed the probe in the center of each region. The regions were sized the way they were because they roughly match the size of a louver I can buy from Trackspec.

So, my winter move is going to be a fiberglass hood with a vent in or around the #5 location. Any closer to the hood and the vent will be far less effective.

Wrinkled Member

Well-Known Member

about 2 posts...the one referring to the t-shirt both can fly that was a t-shirt we did years ago reference to Conleys hood with the vents he got our very lst glass hood and the events as well vents are from an earlier firebird can't member the vintage but it was a stock item on the firebird hoods way back around 1989 or so.